The invention relates to splicing blocks, particularly splicing blocks for use in editing multitrack magnetic sound recording tape.
Specifically, this invention is an improvement over my prior U.S. Pat. No. 2,599,667, issued June 10,1952, which is incorporated herein by reference.
In ordinary single-track tape editing, it is sufficient to edit the tapes at points where sound levels and the sound character insure that a smooth, noiseless cross-fade can be obtained where one sound joins another. In order to accomplish the editing of a single track tape, my prior patent provided adequate means.
Illustrated in U.S. Pat. No. 2,599,667 is a splicing block having a longitudinal groove therein. Further, there is a transverse slit at 90.degree. to the longitudinal groove, as well as a slit at 45.degree. to the longitudinal groove.
While the splicing of a tape at a 45.degree. angle is quite acceptable for single track tapes, it is not acceptable for multitrack tapes. With more than one track of sound recorded on the tape in the same direction, it is necessary that the sound of all tracks be edited within the same instant of time; otherwise, one or more tracks might noticeably lead or lag the others. According to accepted hearing theory, the time segment should be no longer than 0.02 to 0.03 seconds to go unnoticed by listeners with normally acute hearing.
If one cuts the tape during the editing process at 90.degree. using the transverse slit of my earlier patent, there are two phenomena that would cause a noise click to be heard:
(1) Magnetic recording is accomplished by the mixing of bias current and audio currents. When a tape is cut, the inaudible bias current may be cut on one segment where its voltage is above normal, and on another segment where its voltage is below normal. If two tapes to be spliced together exist in this condition, a noise click will be heard from the voltage jump at the splice. Therefore, a slanting cut must be made so that bias voltages present will be averaged and made inaudible at the splice.
(2) In cutting and splicing at 90.degree., some iron oxide may very likely gather at the splice. The gathering of the iron oxide at the splice might, itself, cause noise at the splice. A slanting cut will obviate this effect as well.